A technique disclosed herein relates to an electro hydrostatic actuator (EHA) system for retracting/extending a landing gear of an aircraft.
In recent years, hydraulic supply systems have no longer been mounted in conventional aircrafts, considering improvement of fuel efficiency of aircrafts, maintainability of aircrafts, etc. It has been proposed that EHA systems are mounted as actuators for, e.g., retraction/extension of landing gears, a control surface operation, a braking operation, and a landing gear steering operation (see, e.g., US Patent Publication No. 2011/0107756). The EHA system includes a hydraulic actuator, a hydraulic pump, and an electric motor. The electric motor drives the hydraulic pump to operate the hydraulic actuator. For example, in a mechanism for retracting/extending a landing gear, each of the following actuators may be employed for the EHA system: a gear actuator for lifting/lowering the landing gear; a door actuator for opening/closing a door of a landing gear bay in which the landing gear is stored; and a down-lock release actuator for releasing a mechanism for maintaining a landing gear down state.
The EHA system described in US Patent Publication No. 2011/0107756 includes, for a single hydraulic actuator, a hydraulic supply source having a single hydraulic pump and a single electric motor. As described above, the landing gear retraction/extension mechanism includes at least three types of hydraulic actuators, i.e., the gear actuator, the door actuator, and the down-lock release actuator. Thus, the hydraulic supply source is required for each of the three types of hydraulic actuators. For such a reason, since the EHA system of the landing gear retraction/extension mechanism includes at least three hydraulic pumps and three electric motors, there are disadvantages such as expansion of space occupied by the EHA system and an increase in weight of the EHA system.
Considering the foregoing disadvantages, e.g., Japanese Unexamined Patent Publication No. 2009-047237 describes an EHA system in which a single hydraulic supply source supplies hydraulic pressure to two actuators, i.e., a gear actuator and a down-lock release actuator, operated in synchronization with each other in the operation of retracting a landing gear.